JHM D3 S8 TCU/ ECU Tune - Review
 

There have been some posts asking about this tune and it's effectiveness on the D3. I thought I'd offer up my experience. First off, other than some initial hiccups with ordering and the cable taking a few months to arrive, JHM customer support has been exceptional. They were quick to respond to emails and sent me several different tunes to try on my car. No complaints there.

I'll start with the TCU (transmission control unit) flash. I did this first. To me this is all you absolutely "need" on this platform. Shifting on the D3 is absurdly slow. Even in sport mode, everything gets a little more twitchy in stock form but not necessarily crisp. The TCU flash fixes this. Shifts become firm and quick. It takes the transmission tuning from mediocre to tolerable. My biggest complaint with this powertrain has always been that it's hampered by it's transmission. This makes it so the transmission is no longer a detraction in the experience. If you are budgeting for one or the other and are having a hard time making up your mind, go with the TCU tune and skip the ECU.

Now on to the ECU. Things get a little murky here. My initial tune pinged really bad under part throttle. JHM was initially pretty dismissive of this, stating that it was likely from a car that had major carbon buildup or failing injectors. Nonetheless, they gave me a second flash and that one also had major part throttle pinging. If you're not familiar with pinging or predestination, it's basically where your air/ fuel mixture ignites before it's ignited, generally while the piston is still in the compression stroke. This is not good. I also didn't really agree that this was a result of carbon build-up or failing injectors for two reasons:

1. I can't see how carbon on the intake valves would result in a pre-detonation situation. If anything, they would inhibit air flow, resulting in a richer mixture and a loss in power both from that and the reduced air flow.
2. The problem only occurred at part throttle. At full throttle there was no pinging. ECUs typically have separate wide open throttle programming than part throttle programming. This suggested to me that there was something up with the part throttle tune.

Nonetheless, I conceded that I just bought this car and hadn't done a carbon cleaning on it yet. It's my third S8 and frankly, I was hoping to put that pain off for a bit. But to test their theory I ripped off the top of the engine and found probably the worst carbon buildup I've seen on one of these, and on a car with just 85,000 miles. Yikes. So I did the carbon cleaning, opened the intake and cleaned the carbon buildup out of that as well, replaced all the coils, injectors and a plugs. Put in new air filters, etc. Basically did everything (and more) that you do to one of these to sort it out. After that I took it back out to see if I still had that pinging... and...

I did. As I thought, it's an issue with the tune, not the car. And to be honest, even if it is an issue with the car, I don't feel comfortable running a tune that's so aggressive that any minor hiccup in the car is going to result in it pinging. Likely this is just a result of them commanding too much timing advance as that's one of the few ways to pull more power out of a naturally aspirated engine from a tune.

So JHM sent another file over. I flashed that and boom, no more pinging. So thoughts on the tune itself?

Well, that's where it becomes a mixed bag. It takes TCU flash shifting from OK to harsh. One of the ways companies tune for soft shifts isn't only in the transmission but they pull a lot of timing at the shift points which reduces engine output. I strongly suspect JHM has gotten rid of all of that ignition timing retardation which, combined with the TCU flash, makes the shifts quick and borderline harsh. It kicks you in the rear. At wide open throttle the car feels like it's launching you through the shift. Personally, I love it. This is a fun car for me. It only sees a few thousand miles of year. But if this was my only car, it might annoy me. I almost wonder if just the ECU tune getting rid of that timing retardation at the shift points would be enough to crisp up the shifts, negating the separate TCU tune. It's hard to say.

As far as power increases go, I would say the tune does more to move the power band and keep peak power by way of adjusting when the intake tumblers open and by getting rid of that reduced timing at the shift points. Both of these will make the car feel faster as well as make it objectively quicker without actually raising peak horsepower. Overall, I'm happy with the purchase. It really transforms the car in a way that makes it a little more raw and wakes the powertrain up, something this car sorely needed.

Is the TCU tune workable/compatible with the 4.2 V8? Does the S8 even have a different TCU map ftom the factory over the V8’s?

Honestly I'm not sure. It's been probably seven years since I've had a D3 A8. I don't recall S mode being as aggressive in that car as it is in the S8 though. The transmissions are the same. The only thing I wouldn't be so sure about is the gear ratios. Were it not for that, I'd say flash it and find out.

Great write up Mike - I appreciate the details and your thoughts throughout what you've shared...not sure I'm ready to pull the trigger, but your post answers a ton of questions for me.

Cheers,

It's been a year and I just want to update this for anyone thinking of doing the same. After a year of driving I'm going to say this tune probably isn't the most well thought out setup there is.

I did the TCU tune first. I loved it. If all you're doing is the TCU tune, it's great. The problem is when you add the ECU tune on top of it. One of the ways manufacturers help improve transmission longevity and make shifts more comfortable is by pulling timing at the shift points. It's super effective. Well JHM appears to be adding all that timing right back in, which is fine! It's actually preferred by me and it's a good way to keep the car in the power for longer. Where it becomes an issue is when you start combining that with what is likely raised line pressure in the transmission as a result of the TCU tune.

How does this manifest itself in real life? Super harsh shifts that feel faster but really aren't. They're just wildly more abrupt. You're wondering, how abrupt? It's recommended that you run with your traction control off because it shifts so hard it loses traction in the 1-2 shift and pulls power. That's not good. But beyond that, you're getting absolutely slammed in between the shifts. 1-2 is violent. If you've ever driven an old muscle car with a built transmission, it's right up there with one of those. And practically speaking, it's not any faster and you run the real risk of damaging hard parts in your transmission.

I decided to remove the TCU tune and leave just the ECU. That is the sweet spot for me. There's a marked difference in power plus they manipulate the intake flaps differently so that the car has a really throaty intake sound almost the moment you get on it. If you're an S8 owner, understand that you're not going to make this transmission shift lightning fast. Skip the TCU tune.

Sounds more like JHM don’t really know what they’re doing.

I had some of the described operation as well, it took one custom change on the TCM flash(5-6 shift was very aggressive compared to the rest) to sort that out. Now the TCM sets up shifts at just slightly faster/firmer in lower throttle and keeps the fast shifts when really leaning into it. Half second improvement to 60 from this alone for me.

On the ECM side, this took some more work, but I also have a somewhat different setup than stock. OEM cats are punched out, all post-cat O2 sensors removed, the painfully upstream bank 2 and 4 sensors relocated to where bank 2 and 4 post-cat used to exist, and high flow cats welded in place of the front resonators.

I think 4 revisions later and I'm happy with the ECM.

If you go the JHM tune route, just expect that you may need some minor tweaking, the tuner gave me exactly what I asked for when it turns out the "canned" stage 1 and 2 tunes weren't exactly what I had in mind.

Yeah I mean that's the issue. I'm grabbing an off the shelf tune that needs to be conservative enough to work on a bunch of different cars. If I had it to do over again I'd have something done on a dyno but I'm not aware of anyone that does that.

You mention harsher shifting. How does that impact the engine/transmission mounts along with the center carrier bearing and support? You're adding a lot of new stress to the system it was not intended for. That's gotta be really hard on mounts and joints.